FIG. 6 shows one an exemplary configuration of an optical fiber communication system for a subscriber system. The system proposes a low-speed communication service of POTS (Plain Old Telephone Service) (for example, telephone service, etc.) and a high-speed communication service which is mainly a transmission of video signals, etc.
In the same drawing, optical transmitter-receiver equipment 5 installed in a station 1 is connected to the respective optical transmitter-receiver facilities 5 of a plurality (N units) of subscriber houses 2 via an optical fiber transmission cable 3 and a 1:N star coupler 4, and the optical transmitter-receiver facilities 5 in the station 1 and the respective subscriber houses 2 respectively have an optical wavelength division multiplexer (WDM) 10, 1.times.2 optical coupler 9, laser diode 6, and photo diode 8. Furthermore, FIG. 7 shows optical transmitter-receiver equipment 5 in a subscriber house 2, wherein a light emission drive circuit 12 and a modulation circuit 57 are connected to the laser diode 6, and a reverse bias impression device 13, an optical receiver drive circuit 51 and a receiver demodulation circuit 14 are connected to the photo diode 8. Furthermore, a picture signal receiver such as video 11, etc. is connected to the optical wavelength division multiplexer 10.
In the optical transmitter-receiver equipment 5 in a subscriber house 2, when both communication signal light of wavelength 81 (for example 1.31:m) and picture signal light as non-communication light of wavelength 82 (for example 1.55:m) different from the above communication signal light enter the optical wavelength division multiplexer 10, the same permits the communication signal light of wavelength 81 to be transmitted to the 1.times.2 optical coupler 9 side and, on the other hand, the same permits the picture signal light of wavelength 82 to be transmitted to the video 11 side.
The 1.times.2 optical coupler 9 transmits communication signal light inputted through the optical wavelength division multiplexer 10 to the photo diode 8 side. Furthermore, the 1.times.2 optical coupler 9 is constructed so that transmission light (communication signal light) of wavelength 81, which is transmitted from the laser diode 6, enters the same, wherein the 1.times.2 optical coupler 9 transmits this communication signal light to the optical wavelength division multiplexer 10 side. Transmission of communication signal light by the laser diode is carried out by the light emission drive circuit 12 and modulation circuit 57.
The photo diode 8 functions as a semiconductor light reception element, and if the reverse bias impression device 13 for impressing reverse bias voltage is driven by the light reception drive circuit 51, the reverse bias voltage is impressed to the photo diode 8. At this time, an optical current responsive to the modulation of the communication signal light incident into the photo diode 8 is detected by the reception demodulation circuit 14.
When an optical communication is carried out between the station 1 side and a subscriber house 2 side by a system shown in FIG. 6 using such an optical transmitter-receiver equipment 5, for example, the communication signal light is made incident into an optical fiber transmission cable 3 via the 1.times.2 optical coupler 9 and optical wavelength division multiplexer 10 by driving the laser diode 6 secured at the station 1 side optical transmitter-receiver equipment 5 and transmitted via the optical fiber transmission cable 3. Thereafter, the communication signal light is inputted into the optical transmitter-receiver equipment 5 at the subscriber house 2 side. Thereby, this inputted communication signal light is transmitted to the optical wavelength division multiplexer 10, 1.times.2 optical coupler 9 and photo diode 8 in the optical transmitter-receiver equipment 5 of a subscriber house 2 in order, and the same communication signal light is received by the photo diode 8 and is detected by the reception demodulation circuit 14 as an optical current as described above.
Furthermore, to the contrary, when communication signal light is transmitted from a subscriber house 2 to the station 1 side, the laser diode 6 in the transmitter-receiver equipment 5 of the subscriber house 2 is driven to transmit the communication signal light through the 1.times.2 optical coupler 9 and optical wavelength division multiplexer 10 in order and to transmit the same through an optical fiber transmission cable 3. The communication signal light transmitted through the optical fiber transmission cable 3 is received by the optical transmitter-receiver equipment 5 in the station 1 side in compliance with the same actions as those at the optical transmitter-receiver equipment 5 of the abovementioned subscriber house 2 side.
Furthermore, for example, as shown in FIG. 6, when picture signal light of wavelength 82 is transmitted from a picture signal light transmission device 67 at the station 1 side, this picture signal light is transmitted to the optical fiber transmission cable 3 via the optical wavelength division multiplexer 10 at the station 1 side and is made incident into the optical transmitter-receiver equipment 5 at the subscriber house 2 side. Thereafter, the picture signal light is divided by the optical wavelength division multiplexer 10 and is received by a video 11 at the subscriber house 2 side, wherein the picture signal light is reproduced.
FIG. 8 shows a device configuration of the conventional optical transmitter-receiver equipment 5. As shown in the same drawing, this device forms an optical waveguide circuit 20 having a core 18 on a circuit board 25, and the optical waveguide circuit 20 is constructed so as to form a lower clad layer 27a, a core 18, and an upper clad layer 27b in the order. A fiber-fixing fixture 21, at which two optical fibers 23a and 23b are provided, is provided at one end side of the optical waveguide circuit 20. The respective optical fibers 23a and 23b are optically connected to the core 18 of the optical waveguide circuits 20, respectively.
Furthermore, a laser diode 6 and a photo diode 8 are provided and optically connected to the other end side of the optical waveguide circuit 20 and the laser diode 6 and photo diode 8 are respectively mounted on the circuit board 25 via an electrode pattern 19. Furthermore, the laser diode 6 is connected to the abovementioned modulation circuit 57 and light emission drive circuit 12, which are not illustrated in FIG. 8, via the electrode pattern 19 and the photo diode 8 is connected to the abovementioned reverse bias impression device 13, reception drive circuit 51 and reception demodulation circuit 14 via the electrode pattern 19.
In the device illustrated in the same drawing, the optical waveguide circuit 20 constitutes the abovementioned optical wavelength division multiplexer 10 and 1.times.2 optical coupler 9, and the optical wavelength division multiplexer 10 has a communication light selective transmission filter 24 inserted into a filter groove 22 of the optical waveguide circuit 20. The communication light selective transmission filter 24 is able to transmit the communication signal light of wavelength 81 and reflect the picture signal light of wavelength 82.
In a case where the optical transmitter-receiver equipment 5 is configured as shown in the same drawing, as both the communication signal light of wavelength 81 and the picture signal light of wavelength 82 enter the optical transmitter-receiver equipment 5 from the optical fiber 23a, the picture signal light of wavelength 82 of these rays of light is reflected by the communication light selective transmission filter 24 of the optical wavelength division multiplexer 10 and is caused to outgo from the optical fiber 23b, and the communication signal light of wavelength 81 passes through the communication light selective transmission filter 24 and enters the 1.times.2 optical coupler 9, wherein the same enters the photo diode 8 via the 1.times.2 optical coupler 9. Furthermore, the communication signal light of wavelength 81 transmitted from the laser diode 6 passes through the communication light selective transmission filter 24 after passing through the 1.times.2 optical coupler 9, and the same is caused to outgo from the optical fiber 23a.